1. Field of the Invention
This invention relates to leak detection systems and more particularly to leak detection systems for gloves utilized with isolator barrier systems.
2. Description of the Related Art
Certain manufacturing processes require the maintenance of separation between two environments to avoid contamination of the cleaner of the two environments by the dirtier of the two. This is accomplished with the use of environments, such as isolation barriers also commonly known as gloveboxes or simply isolators. For example, in the case of certain pharmaceutical products, the manufacturing process is perfomied within these isolation barriers to prevent contamination of the product being produced by dust particles, bacteria and viruses that are found in the outside ambient air. This type of application is commonly referred to as an aseptic application of isolation barriers. The same holds true for the assembly of certain medical devices. In the case of radioactive operations or bacteriological procedures, the environment within the isolation barrier is dirty as compared to the outside ambient air. In these cases, the isolation barrier serves the function of keeping the product being handled from escaping into the external environment and they are commonly referred to as containment applications of isolation barriers.
In recent years, in the pharmaceutical industry, because of the expense and operational difficulties of maintaining so-called “clean rooms” into which operators enter to carry out procedures, the use of isolation barriers has become common practice. The isolation barriers, in concept large glove boxes, are integrated onto the machinery used to carry out the necessary manufacturing operations. A variation of these isolation barriers is what is commonly known as a RABS, Restricted Access Barrier System.
To facilitate viewing of the interior of such isolation barriers by technicians, its walls are commonly fabricated of transparent materials, such as glass or polycarbonate sheet. If an opaque material is used, for example stainless steel, appropriate viewing windows are provided. The walls of the barrier isolators are commonly fitted with a plurality of ports in which a glove is secured such that a technician may insert his hands into the port and perform manipulative operations within the enclosure.
Two types of glove devices are currently used in the industry. A first type, commonly known as a one-piece gauntlet, is a single piece device that includes a glove end fitting the user's hand, a sleeve portion that covers the arm of the user and a port interface portion that connects directly to the port itself. The gauntlet is fabricated of homogeneous rubber material that provides the imperviousness while permitting the necessary level of dexterity to the operator.
A second type of glove device is a two-piece glove/sleeve assembly. This device consists of a glove end that covers only the hand of the operator. It is fabricated of homogeneous rubber material and provides the necessary level of dexterity to the operator. The glove is attached to a plastic cuff by means of a clamping devices such as a rubber “O” ring. The cuff is then attached, also In sealing fashion, to a sleeve attached to the barrier isolator wall. The sleeve is fabricated of somewhat tougher material than the glove with a resulting better resistance to damage.
Both the one-piece gauntlet and the two piece glove/sleeve assembly permit the access of the operator into the internal volume of the barrier isolator to the point that the operator's shoulder fits within the opening of the port itself.
Examples of glove and port types are those disclosed in U.S. Pat. No. 4,010,588, U.S. Pat. No. 4,089,571, U.S. Pat. No. 4,141,609 and U.S. Pat. No. 5,578,747.
The operative manipulations that the operator typically conducts using the gloves of the barrier isolator involve the handling of components that can cause damage to the glove itself. Such damage may range from an obvious visible tear—to a miniscule, invisible to the naked eye, pinhole. A glove integrity breach is a major concern for both applications of barrier isolators. In the case of an aseptic operation, the operator's hand that is by definition “dirty” can come into contact with the breach thus creating the possibility of contaminating the product within the barrier isolator chamber. In the case of containment applications, the breach can allow the compound being contained within the barrier isolator to escape with a resulting hazardous exposure to the operator.
The above clearly explains the need for a means of detecting such integrity breaches in the gloves and sleeves of barrier isolators, in particular those breaches that are not clearly visible to the operator. One can also appreciate the need for being able to test the integrity of such glove devices in-situ, meaning while they are installed onto the barrier isolator, and the barrier isolator is in operation (meaning that it is either sterile or contains a dangerous compound).
Numerous technologies have been developed for the purpose of detecting pinholes in rubber gloves. Japanese Patent JP04151849 discloses a system in which the glove under test is filled with water and placed under vacuum. Water detection outside the glove is indicative of a breach. Another technology is disclosed in Japanese patent JP07128179 in which hot gas is blown into the glove and a temperature gradient on the outer surface of the glove under test is an indication of a defect. Another technology is disclosed in Japanese patent JP07218377 in which ultrasonic waves are used to detect the presence of a breach. Japanese patent number JP56140232 discloses a system in which light detection within the glove is used for the same purpose. Also, in Japanese patent JP09079810, a breakdown of the dielectric properties of the material at the location of the breach is used for the detection.
Another technology that evaluates the integrity of containers that are flexible in nature is that disclosed in U.S. Pat. No. 5,287,729 and U.S. Pat. No. 6,202,476. This technology makes use of the physical deformation of the flexible portion of the container under test to make a determination as to its integrity. Such technology would encounter difficulties in its adoption for testing gloves because of the rubber material of the glove and the inherent unpredictable physical behavior of the material itself. U.S. Pat. No. 5,600,996 discloses an additional technology that is not conducive to leak testing of a rubber glove because it relies on the volumetric behavior of the test part when compared to a standard part of identical volume. The rubber material of the glove does not permit the use of physical characteristics to determine test part integrity.
Bubble leak detection is a commonly used technology for leak testing of rubber gloves. This technology is disclosed in Japanese patent number JP05010843. This technology uses the visual detection of air bubbles escaping through breaches in the glove while the glove is submerged in fluid and pressurized to a given pressure level. A variation of this technology is that disclosed in U.S. Pat. No. 4,776,209 in which the glove is not submerged in fluid but, nevertheless, bubbles are visually detected in the apparatus when a breach is present in the glove under test. Although reliable and widely used, this technology has the inherent limitation that the detection of a breach is ultimately left up to the visual observation by the operator, with the related human factor reliability limitations. In addition, the use of a fluid in a production environment can be operationally limiting and unfriendly.
Tracer gas technology is widely used for container leak testing purposes in many industries. The technology is based on the principle that, if a breach exists in a part, the test gas of choice, for example helium, nitrogen or oxygen, will pass through the breach and will be detected by an appropriate sensor. An example of this technology is that disclosed in U.S. Pat. No. 6,354,142. In this patent, the tracer gas is contained within the container under test. Its detection is indicative of a leak if the container is placed under appropriate pressure within a sealed chamber. Although extremely sensitive and therefore susceptible to “false” positives due to the nature of the test approach itself, tracer gas technology can be adapted to rubber glove leak testing purposes as demonstrated in U.S. Pat. No. 5,578,747. This patent applies directly to the field of the current invention and uses oxygen detection within a chamber that is evacuated with nitrogen prior to the testing of the glove. A different example of the use of this technology for the purpose of detecting breaches in gloves is that disclosed in the International Publication WO 00/27478. This patent demonstrates how a breach in the glove can be found by detecting the presence of oxygen within a gap between an inner and outer layer of the glove after this gap is purged of oxygen with an inert gas, such as nitrogen.
Another technology that is adopted for leak testing of gloves is that of leak rate detection. This technology is based on the inflation of the test part to a given pressure value and measuring the gas flow rate required to maintain such pressure level. If this measured flow rate is higher than some predetermined value, the part under test is deemed to be defective. U.S. Pat. No. 4,942,758 is an example of a high speed, automatic application of this technology. The part is placed under pressure and the flow rate required to apply this pressure is compared to a threshold. The same technology, but different means of applying it, is that disclosed in U.S. Pat. No. 5,546,789. The '789 device uses a bell jar enclosing of the test part that is pressurized to a given value so that, if leaking, it causes an airflow into the bell jar that is detected by an appropriate flow meter and includes an offset flow rate to compensate for possible leaks of the test apparatus itself. U.S. Pat. No. 6,584,828 describes an additional use of this technology where the unit under test is placed under pressure and is determined to be leaking if the air flow entering the chamber is measured to be above a certain threshold value. The three US patents listed above describe in detail the extensive use of modern sensor technology, calculating systems, electronics and software that permit the implementation of the technology in a production environment by providing the appropriate feedback of the test's outcome to the operator. The leak rate detection method for detecting leaks in a test item works very well in those applications where the item under test is rigid in its physical construction therefore occupying a consistent, fixed volume. It is much more difficult to apply this technology to the testing of rubber components, such as barrier isolator gloves. The stretching and eventual creep that goes on in a rubber device once positive or negative pressure is applied to its surfaces make achieving a precise reference pressure very time consuming. Time management is an important factor in any manufacturing operation. Nevertheless, Japanese Patent 2002-280277 demonstrates the application of this technology to negative pressure testing of the barrier isolator glove. The glove under test is placed inside a vacuum chamber while it is still attached to the isolator wall. It is placed under negative pressure of a given value and the flow rate is compared to an acceptability threshold.
The Swiss company SKAN AG produces a glove leak tester that adopts the leak rate monitoring technology to determine whether the glove under test is to be rejected. The glove under test is pressurized to a given reference pressure by using the air enclosed in a pressure chamber. Flow will occur between the pressure chamber and the glove under test until equilibrium is reached. This equilibrium will not be reached if a breach is present in the glove under test. The Skan system incorporates a number of control system features that aid the operational aspects of the device in the manufacturing environment.
Another technology that is widely used to test the integrity of containers is that of pressure decay. The internal volume of the part under test is pressurized to a threshold value and then sealed off. The amount of pressure decay over a set time duration is indicative of whether the part is leak tight. Pressure decay testing of the integrity of a test container is well demonstrated in U.S. Pat. No. 6,662,634. In the system disclosed in that patent, a pressure profile graph of the test cycle is provided to clearly show the behavior of the pressure as it drops over time after the inflation air supply is shut off. The part under test is placed under positive or negative pressure and the pressure value at the end of the test is electronically compared to a stored pass/fail value to determine the test outcome. Air temperature changes during the pressure decay cycle have an impact on the accuracy of the test results. As air is compressed to pressurize the part under test, its temperature rises. As the pressure drops as result of the test, the air temperature drops as well. This causes an error in the pressure value that is not related to the leak testing process. U.S. Pat. No. 5,065,350 adds temperature compensation to the pressure decay process to address the impact of air temperature fluctuations during the test by adding a compensating factor to the pressure values obtained during the test.
Pressure decay technology has been adopted for glove integrity testing. U.S. Pat. No. 4,206,631 applies to the field of surgical glove testing and addresses the expandable nature of the rubber glove by restraining the part under test in a clam shell of appropriate geometric configuration and inflating the part under test to values beyond the point of rupture to address the effect of stress relaxation and creep that is inherent to stretching of rubber like components. Another example of pressure decay testing of a rubber glove is that shown in the Japanese patent number 2002-131171 in which a method for attaching and sealing to the part under test is demonstrated. Japanese patent 06-75092 demonstrates a similar pressure decay application except that the part under test is placed is placed under vacuum rather than positive pressure. U.S. application Ser. No. 2004/0149014A1 demonstrates the application of pressure decay technology to integrity testing of gloves of a barrier isolator. This patent publication describes, in detail, the means for in-situ sealing the part under test from the surrounding environment for the purpose of conducting the test. The test method is defined as simple monitoring of the glove internal pressure by means of a pressure gage to detect the pressure drop that is indicative of a leak.
U.S. Pat. No. 5,412,978 discusses integrity testing of a test part using either a leak flow rate detection or pressure decay detection but it also provides means for accelerating the leak test process by separating the process in three distinct phases and forcing the transfer from one phase to the next by detecting flow rate into the test part rather that a fixed time duration. The '978 patent stresses the need to be able to perform the leak test in as short a time as possible because of manufacturing efficiency reasons.
Accordingly, there is a need for a glove leakage detection method and apparatus that can deal with the stress relaxation and creep characteristic of rubber gloves, operates in a static or equilibrium mode rather than dynamic mode and permits trending of the test values to shorten leak test times.